Accuphase E-550 Brochure
● Revolutionary AAVA volume control ● Power MOS-FETs in triple
parallel push-pull configuration driven in pure class A ● Current feedback
principle and MCS+ topology in power amplifier section ● Logic-control
relays for straight and short signal paths ● Sturdy power supply with
large toroidal transformer and high filtering capacity ● EXT PRE button
allows independent use of preamplifier and power amplifier sections
The ultimate integrated pure class A amplifier – Power MOS-FETs arranged
in triple parallel push-pull configuration. Innovative AAVA volume control.
Strong power supply with large toroidal transformer and high filtering capacity
supports linear output progression of 120 watts/ch into 2 ohms, 60 watts/ch
into 4 ohms, or 30 watts/ch into 8 ohms. Power amp section uses current feedback
for optimum high-frequency phase characteristics and MCS+ topology.
The first integrated pure class A amplifier from
Accuphase, the E-530, drew a lot of attention and
praise. The E-550 now takes over as a further
improved and fully redesigned successor model.
It stands at the pinnacle of integrated amplifiers,
featuring latest technology and strictly selected
high-quality parts. For the first time in an integrated
amplifier, it offers the revolutionary AAVA type
volume control. In AAVA, amplification and volume
control are fully unified, and no variable resistors
are used. This ensures excellent sound quality and
performance, but the circuitry requires a
considerable amount of space. In order to enable
the use of AAVA in an integrated amplifier,
advanced design know-how and mounting
technology were brought into play, to increase
component density while keeping sonic purity and
performance at the high level that is the hallmark
of Accuphase. The result speaks for itself.
The power amplifier section features the highly
acclaimed current feedback principle developed
by Accuphase, as well as further improved “MCS+”
circuit topology, for even better electrical
characteristics. The output stage devices are
AAVA (Accuphase Analog Vari-gain Amplifier) volume control
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■ Volume control resolution
■■
AAVA adjusts the listening volume by means of 16 current switches which are
operated by 16 weighted V-I converter amplifiers. The number of possible volume
steps set by the combination of these converter amplifiers is 2 to the power of
16 = 65,536.
■■
■ AAVA maintains high S/N ratio and uniform frequency response
■■
With conventional volume controls, the impedance increases significantly at
settings that correspond to normal listening levels, thereby leading to increased
noise. Because AAVA performs adjustment by selective use of V-I converter
amplifiers (changing the actual gain), there is no change in impedance and
thus no deterioration of S/N ratio or alteration of frequency response. Changing
the volume with AAVA does not mean introducing noise or detracting from the
high performance of the amplifier.
■■
■ Same operation feel as a conventional high-quality volume control
■■
The volume control knob position is detected by a dedicated CPU which in
turn selects the current switches for AAVA operation. Operating the knob
therefore feels exactly the same as with a conventional control, and as before,
operation via the remote commander is also possible.
power MOS-FETs famous for their musical
qualities, arranged in a triple parallel push-pull
configuration and driven in pure class A. Low
output impedance and constant voltage drive
ensure superb speaker control. The large highefficiency toroidal transformer (430 VA) in the
power supply, along with eight 10,000 µF filtering
capacitors selected for their sonic properties
support linear progression of output regardless of
impedance, with a per-channel rating of 120 watts
into 2 ohms, 60 watts into 4 ohms, or 30 watts into
8 ohms.
■■
■ Simple circuit configuration
■■
AAVA unifies the amplifier and volume control functions, resulting in a circuit
that is electrically very simple. Long-term reliability is excellent, with performance
and sound quality that will remain unchanged also after prolonged use.
■■
■ AAVA means analog processing
■■
The AAVA circuit converts the music signal from a voltage into a current,
switches gain by means of current switches, and then reconverts the current
into a voltage. The entire process is carried out in the analog domain.
■■
■ No more left/right tracking differences or crosstalk
■■
Because AAVA is an electronic circuit employing highly precise metal film
resistors, there is virtually no left/right tracking error also at low volume levels.
Since channels can be kept separate, crosstalk also does not present a problem.
■■
■ Attenuator and balance control also implemented by AAVA
■■
The functions of the attenuator and the left/right balance control are covered
by the AAVA circuit as well, eliminating the need for additional circuit stages.
Keeping the configuration simple helps to maintain high performance and sonic
purity.
16 current switches
(65,536 possible combinations)
BUFFER
INPUT
Input music
signal
V- I Converter
Conversion into current with 16
weighting stages (1/2 - 1/216)
Volume
Balance
CPU
Attenuator
CPU detects position of volume
knob and operates current on/off
switches according to knob position
Current values
are added
AAVA operation
AAVA operates by feeding the music signal to a V-I (voltage - current) converting amplifier
where it is weighted in 16 steps [1/2, 1/22, ... 1/215, 1/216]. The 16 current steps are turned
on or off by 16 current switches, and the combination of switch settings determines the
overall volume. The switching operation is controlled by a CPU according to the position of
the volume control knob. The combined signal current forms a variable gain circuit that
adjusts the volume. Finally, the combined current is converted back into a voltage by an
I-V (current - voltage) converter.
I-V Converter
Reconversion of
current into voltage
Volume knob is turned
and position is detected
The newly developed volume control called AAVA (Accuphase Analog
Vari-gain Amplifier) is totally different from conventional controls using
resistors. Because the music signal does not pass through variable
resistors, it is not affected by changes in impedance. This means that
high signal-to-noise ratio and low distortion of the signal are maintained.
Adjusting the volume does not introduce any deterioration in sound quality.
■■
■ AAVA control assembly with
■■
OUTPUT
three AAVA units and CPU
arranged neatly on a motherboard
■■
■ Output
■■
amplifie
triple p
power M
mounte
sink
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